The former chairman of Donald Trump's presidential campaign, Paul Manafort, has been indicted on numerous charges, including conspiracy against the United States, money laundering, tax fraud and making false statements to federal authorities. Special Counsel Robert Mueller revealed the 12-count indictment Monday morning. Also charged was Manafort's longtime aide, Richard Gates, whom the indictment refers to as Manafort's "right-hand man."

Additionally, the special counsel's office revealed that another Trump campaign associate, George Papadopolous, had pleaded guilty on October 5 to making false statements to the FBI in January regarding his contacts with Russia. Papadopolous was a foreign policy adviser to the campaign, and is an international energy lawyer.

The indictment does not address the presidential campaign directly, nor does it mention the president. Rather, the focus is on Manafort's earlier lobbying work in Ukraine, for which he allegedly received millions of dollars that he then hid from tax authorities using various tax shelters. "Manafort used his hidden overseas wealth to enjoy a lavish lifestyle in the United States without paying taxes on that income," the indictment says.

Manafort spent years working for a pro-Russian political party in Ukraine, possibly against the interests of the United States. Some of the charges brought in the indictment date back a decade.

Manafort, who held his post as the Trump campaign chairman from June through August 2016, and Gates are set to appear before a federal magistrate Monday afternoon.

Mueller was assigned as Special Counsel in May to investigate Russian meddling during the 2016 presidential election. American intelligence agencies agree that the Russian government, all the way up to and including President Vladimir Putin, tried to interfere with the election by hacking and releasing emails related to Hillary Clinton's campaign and by spreading false information across social media. These are the first charges Mueller's team has announced in connection to that probe, but they are not expected to be the last.

President Trump, who has long denied any collusion between himself or his campaign and Russia, responded via Twitter, saying that the charges are not related to the Trump campaign, adding "No collusion" in a follow-up tweet.

In a related matter, a former Trump campaign foreign policy advisor, George Papadopolous, has pleaded guilty to lying to the FBI regarding his contacts with Russian government officials during the campaign. Papadopolous admitted that he lied to authorities regarding his contacts with a Russian professor whom he knew had "substantial connections to Russian government officials," according to the indictment.

UPDATE 3:30 P.M. ET: Manafort and Gates pleaded not guilty at their mutual appearance in federal court this afternoon. Government lawyers requested house arrest for both men, due their high risk of flight, which the judge granted. Bail was set at $10 million for Manafort and $5 million for Gates.

If convicted, Manafort could face up to 12 to 15 months in prison. Gates possibly faces 10 to 12 years.